Science fiction is the genre of speculative fiction that imagines advanced and futuristic changes in technology, scientific knowledge, or biological systems. The elements common to science fiction have increased over time: from space exploration, extraterrestrial life, time travel, and robotics; to parallel universes, dystopian societies, and biological manipulations; and, most recently, to information technology, transhumanism, posthumanism, and environmental challenges. Science fiction often explores human responses to the consequences of these types of projected or imagined scientific advances.